1. Field of the Invention
The present invention relates to a force sensor protection mechanism that protects a force sensor against an overload, an end effector having a force sensor protection mechanism, and a robot arm having a force sensor protection mechanism.
2. Description of the Related Art
In industrial robot apparatuses or the like, sometimes, a force sensor is installed between a robot arm and an end effector, force given to a work object by the end effector is detected, and work is performed while adjusting this force. In general, many force sensors calculate force acting on the force sensors on the basis of the change in physical quantity such as the stain of a member. In order to obtain high sensitivity to a weak force or a minute change, the sensitive member of a force sensor is reduced in rigidity, is made easily deformable, and is made frail so that the quantity of strain (the change in physical quantity) of the member is increased.
However, since a force sensor is frail, the force sensor may break down when an overload is applied to the force sensor. So, a force sensor protection mechanism intended to reduce the labor for repair or replacement has been proposed.
Japanese Patent Laid-Open No. 2004-174696 discloses a robot arm in which an arm, a force sensor, and an end effector are connected. By engaging an active engaging member fixed to the arm and a passive engaging member fixed to the end effector with each other, the arm and the end effector are fixed to each other, and by disengaging them from each other, the force sensor is made operable.
In recent years, manipulators have been required to be capable of highly accurate positioning so that they can perform more precise work, and the manipulator tip position when a force acts has been required to be highly accurate and to be small in the amount of displacement. That is, a force sensor has been required to be small in the amount of displacement, to have high rigidity, and to be capable of sensitive measurement despite its high rigidity. Therefore, a force sensor protection mechanism has been required to be highly accurate so as to prevent a member that is small in the amount of displacement from being excessively strained. Under these circumstances, a force sensor is configured to be capable of sensitive measurement despite the high rigidity of the sensitive member and the small change in physical quantity in response to acting force.
In order to manufacture an active engaging member and a passive engaging member with a high degree of accuracy, processing accuracy and assembly accuracy need to be increased. However, there is a limit, and a manufacturing error occurs. In a system in which an arm, a force sensor, and an end effector are connected, the force sensor is subject to constraint by engaging an active engaging member with a passive engaging member. If there is a manufacturing error in the active engaging member and the passive engaging member, the force sensor is constrained in a deformed state owing to the manufacturing error, and an overload continues to be applied to the force sensor. The force sensor in an overloaded state breaks down easily. If the force of engagement between the active engaging member and the passive engaging member is weakened, they do not function as a force sensor protection mechanism.